The overall goal of this research program is to study cellular mechanisms of hormone action on sexual and aggressive behaviors in female Syrian hamsters. It is proposed that aggression is an integral component of social behaviors of females in general, and that the results of these studies will be generalizable to females of other species. One focus of these experiments is the identification of a novel functional neural pathway related to the control of aggression in female hamsters. Since factors regulating aggression in females are rarely studied, it is not surprising that nothing is known about the neural pathways underlying female aggression. Related to this goal, the experiments in Section I will focus on afferent and efferent pathways of the ventromedial nucleus of the hypothalamus. This nucleus was chosen for its unique position as the primary site of action of ovarian hormones on aggression and sexual behavior in female hamsters. In Section II, chemical lesions will be made in neural regions that interact monosynaptically with the ventromedial hypothalamus. Lesion sites that produce effects on sexual behavior and aggression will help to define functional pathways for these behaviors, including points of convergence and divergence in the neural control of these behavioral systems. In Section III and IV, studies will examine possible mechanisms through which ovarian hormones can determine the female's behavioral state. In Section III, the possibility that steroids produce dedritic reconfigurations in neurons of the ventromedial hypothalamus will be examined. In Section IV, the effects of steroids on the ultrastructure of neurons in the ventromedial nucleus of the hypothalamus will be assessed. The goals of these sections are 1) to infer biochemical processes in nerve cells stimulated by steroids, and 2) to relate these changes in structure to the behavioral effectiveness of such steroid treatments. In sum, the results of these studies will identify neural systems related to the control of sexual behavior and aggression in females, including ways in which hormones may alter the functional nature of these systems, and therefore, behavior.